In conventional elevator systems, elevator car doors are selectively opened and closed by a rotary electric motor driving mechanical assemblies, which typically include a plurality of moving parts such as gear boxes, a set of drive arms, and linkages. The major drawback to the existing elevator car door systems is their susceptibility to misalignments, which necessitate adjustments and result in high maintenance costs. Also, the misalignments degrade the performance of the system such that the doors' opening and closing functions are not consistently smooth.
Linear motors ca n potentially provide an alternative to the conventional door operating systems by eliminating the mechanical linkages and problems associated therewith. Linear motors typically include a motor primary unit and a motor secondary unit. The motor secondary and the motor primary move past each other to open and close elevator car doors. Typically, linear motors have a much larger magnetic air gap between the parts of the motor than do conventional rotary motors. To compensate for the larger air gap, linear motors must operate at a much higher current level than conventional motors. The greater current level generates heat and may result in overheating. The problem of overheating in linear motors of elevator car door systems is exacerbated because the linear motor is situated in a limited space environment and the heat cannot dissipate easily. Overheating is highly undesirable because it results in efficiency losses and can cause a short circuit. Therefore, a temperature rise in near motors must be controlled.